Various types of jars have been used commercially during drilling and logging operations. Mechanically actuated jars have been used for decades in downhole operations to break loose a tool struck in a well. A mechanically actuated jar may be suspended in a well from a wireline, and utilizes two energy sources for the jarring effect: (1) stored energy within springs within the tool; and (2) the wireline acting like a spring. Both sources of energy may be released when tension reaches a selected level. Stronger grades of wireline have been introduced recently with breaking strength up to 28,000 pounds. The stronger wireline and wireline connectors mean operators can pull harder from the surface to free logging tools stuck downhole.
A wireline hydraulic jar also utilizes the stored energy of a spring to produce part of an impact, but relies primarily upon metering fluid through an orifice in the tool in order to release a mass which creates the jarring force. Hydraulic jars have also been used in the past with an enhancer, which is basically an inverted hydraulic jar with its own set of springs and no hammer release mechanism. A hydraulic jar can become more effective with the additional mass of both the jar and the enhancer. A mechanical jar relies primarily on the impact (initial hit) of the jar, but does deliver both an impact and a short impulse. Mechanical jars have proven to be maintenance intensive, and are not widely favored compared to hydraulic jars. Hydraulic jar components are effectively sealed within a housing from downhole fluids, and thus have a high reliability and less maintenance. A significant advantage to the hydraulic jar is its timed release capacity, which allows the operator to make a variable pull and therefore achieve a maximum pull with maximum impact.
When a jar is activated, impact is the initial instantaneous force generated by the jar. Impulse is a residual force of the impact, consisting of reverberations occurring in milliseconds following an activation. The objective of a jar is to create the strongest impact possible and the strongest and longest impulse. The impact of a mechanical jar is preselected value before running the jar in the hole. The selected value cannot be changed unless the tool is retrieved to the surface. A hydraulic jar, on the other hand, can vary the jarring force by varying the pull exerted on the wireline while fluid is metered past the piston. A hydraulic jar may therefore produce a significantly greater impact and a significant impulse compared to a mechanical jar.
Operators have commonly used jars in the past when a tool or drill string becomes stuck in a well. Tools which frequently become stuck in the hole include formation testers, density/neutron tools and resistivity tools. More recently, operators are requesting the inclusion of a jar when tools or drill strings which are susceptible to becoming lodged in a well are used, so that the jar will already be in place if the tool or drill string becomes stuck in the well. The benefits of using a wireline instrument to log oil and gas wells quickly diminishes if the logging string frequently becomes stuck in the well. As wells become deeper with more complex well designs, improved jarring tools are required to ensure that these logging tools can be retrieved successfully. A drill string stuck in a well may cost an operator hundreds of thousands of dollars to free. It is now even more important to run the jars with the logging tool or drill string since freeing a drill string or logging tool typically becomes more difficult the longer the drill string or logging tool is stuck in the well.
U.S. Pat. No. 3,987,858 discloses a hydromechanical drilling jar consisting of a hydraulic jar for an upward jarring motion and a mechanical jar for a downward jarring motion. The release of tension in the drill string contributes to an upward jarring blow when fluid flows around a piston. If the jarring blow does not release the stuck object, a downward jarring will be effected with the mechanical jar section.
U.S. Pat. No. 4,109,736 discloses a double acting hydraulic jar capable of applying an upward jarring action and a separate downward jarring action. U.S. Pat. No. 4,807,709 discloses a fluid activated jar that utilizes drilling fluid to open and close the jar. U.S. Pat. No. 4,226,289 discloses a hydraulic jar capable of being automatically reset to deliver a plurality of jarring motions. The tool is intended to jar up and jar down utilizing the appropriate hydraulic jar section of the tool.
The benefits of a hydraulic jar are discussed in an article entitled “New Jar Technology Minimizes Risks of Unproductive Rig Time in Well Logging Operations.” Other patents of interest include U.S. Pat. Nos. 6,290,004, 6,164,393, 6,206,101, 4,478,284, 4,200,158 and 3,570,611.
The disadvantages of prior art are overcome by the present invention. An improved multiple impact hydraulic jar assembly and method are hereinafter disclosed capable of producing two or more jarring actions with a selected short time delay between the jarring actions.